The present invention relates to a process for the inspection of the surface of a member by means of an eddy current transducer supplying a signal representing the state of said surface, as well as to devices for performing such a process.
It is at present standard practice to inspect the surface of members made from electrically conductive materials by using eddy current transducers. The signal supplied by the transducer gives information on the surface state and the possible presence of defects in the surface. For example, an inspection of this type is carried out periodically in the tubes of heat exchangers or steam generators of nuclear power stations. However, This application is in no way limitative and surface inspections by means of eddy current transducers are carried out in numerous other fields.
Whatever the application, the hitherto used inspection procedure consists of carrying out a maximum complete scan or sweep of the surface to be inspected and observing by means of a direct reading system variations of the signal supplied by the transducer in order to deduce the state of the inspected surface.
Although this inspection procedure has hitherto been used in a standard manner, it has a certain number of disadvantages linked with the need of adapting the transducer and the path followed by it to the size and orientation of the defects. Thus, for easy detection of the defect, the size of the transducer must be as close as possible to that of the defects to be detected. Moreover, when investigating point defects, differential transducers are used, which must be oriented in such a way that the direction linking the two windings forming the same coincide with the axis having the greatest variation gradient of the signal supplied by the transducer. However, there are at least two cases where these conditions cannot be satisfied:
(1) When neither the size nor the orientation of the defects is known. PA1 (2) When the path taken by the transducer is already established.